A number of catalytic processes are employed in the petroleum industry for the purpose of converting crude petroleum to a variety of products having physical and chemical properties which make them suitable for use by consumers. Among the refining processes involving the use of catalysts are hydrocracking, hydrodesulfurization, hydrodenitrification and reforming. In these and other refining processes where catalysts are employed, the catalysts decline in activity during the course of use as a result, in major part, of accumulation of carbonaceous matter commonly containing hydrogen and sulfur on the catalyst surface and in the catalyst pores. A number of catalysts used in a number of the processes lose activity rapidly during the course of use and the plants in which such catalysts are employed commonly have provision for regeneration of the catalyst either in the reaction vessel itself or in an adjacent regenerator vessel to which the catalyst is transferred continuously as it is used. There are a number of catalysts, however, which are used for extended periods before they become deactivated and which continue to be effective until the build-up of carbonaceous material on the catalyst is very high. Onstream periods of months, or even years, are observed in some of the processes. In these cases, the refining units do not ordinarily include provision for catalyst regeneration and the refiner commonly discards the catalyst when it has completely lost activity and replaces it with a new charge or the catalyst may be removed from the refining unit and regenerated in a regeneration unit which is neither attached nor related to the refining unit from which the catalyst is taken.
Catalysts containing metals of groups VIb, VIIb and VIII of the periodic table, such as cobalt, nickel, tungsten, molybdenum, or mixtures of two or more of these metals supported on a conventional support such as alumina, are commonly employed in hydrodesulfurization of various petroleum streams, hydrodenitrification of such streams and in hydrocracking high boiling petroleum streams which are previously treated to reduce sulfur and nitrogen contents. These catalysts are commonly used for extended periods before they become so deactivated by accumulation of carbonaceous deposits that they can no longer be used.
A great number of methods for regenerating catalysts which have become inactive due to the accumulation of carbonaceous material on their surfaces have been described. In nearly all of these processes, the regeneration is accomplished by contacting the inactive catalyst with a free oxygen-containing gas at elevated temperature to burn the carbonaceous material from the catalyst surface. Process conditions in the various methods differ widely. The oxygen content of the regenerating gas may vary from a very low level, below one volume percent, to very high levels in which the oxygen content is above 20%; the temperature at which the regeneration burn is carried forward is varied over a considerble range, the pressure maintained in the regeneration zone is varied over a wide range from slightly over atmospheric pressure to several hundred psig. and the volume of regenerating gas contacted with a given volume of catalyst per unit time is also varied widely. Various combinations of operating conditions are selected which are adapted to fairly completely burn the carbonaceous materials from the catalyst surface without experiencing temperature excursions and resultant sintering of the catalyst particles, but use of a free oxygen-containing gas to cause combustion of the carbonaceous deposits on the catalyst is common to nearly all of them. The difficulty of regenerating a catalyst contaminated with carbonaceous material generally varies with the level of carbon contamination and this level varies with the character of the hydrocarbon feed which has contacted the catalyst and the length of time during which the catalyst has been kept in service. More heavily contaminated catalysts require more time for regeneration and show less recovery of activity.
Pursuant to the present invention, carbon contaminated catalysts which are susceptible to reactivation by burning the carbonaceous deposits from their surfaces are subjected to a pretreatment before being contacted with a free oxygen-containing gas at a temperature adapted to cause burning to the carbonaceous deposits with the result that a greater proportion of initial activity is restored to the catalyst.